Transcript Slide 1

Grotzinger • Jordan • Press • Siever
Understanding Earth
Fifth Edition
Chapter 14:
EXPLORING EARTH’S INTERIOR
Copyright © 2007 by W. H. Freeman and Company
Concepts we will use in this class
In bold are the ones I consider most important
Compressional wave
Conduction
Convection
Core-mantle boundary
Depositional remanent magnetism
Dipole
Geotherm
Lower mantle
Low-velocity zone
Mohorovičić discontinuity (MOHO)
Paleomagnetism
Phase change
Principle of isostasy
Seismic tomography
Shadow zone
Shear wave
Thermo-remanent magnetization
Lecture Outline
1. Exploring the interior with seismic waves
2. Layering and composition of the interior
3. Earth’s internal heat and temperature
4. 3-Dimensional structure of the mantle
5. Earth’s magnetic field
Chapter 14
Exploring
Earth’s
Interior
Background facts about Earth’s Interior
• The center of the Earth is about 6400 km
below us … the deepest well is 10 km.
• Heat inside the Earth drives the core’s
geodynamo and the mantle’s convection.
• Earth’s interior is explored by using
information from seismic waves and their
passage through the body of the Earth.
1. Exploring the interior with seismic
waves
● Basic types of waves
● compressional (P waves)
● shear (S waves)
● Reflection and refraction
1. Exploring the interior with seismic
waves
● Paths of seismic waves
● wave bending (refraction)
● shadow zones (P and S)
● reflection at internal
boundaries
P-wave
paths
S-wave
paths
P- and
S-wave
paths
from an
earthquake
P-, S-, and surface wave
paths: from focus to seismograph
P-, S-, and surface waves
recorded on a seismograph
2. Layering and composition of the
interior
(a.k.a. Seismology model of Earth’s
layers)
● crust and lithosphere
● asthenosphere
● mantle with internal phase
change at 400 km
2. Layering and composition of the
interior
● Seismology model of Earth’s
layers
(continued)
● core-mantle boundary
● core (inner and outer core)
Earth’s
layering
revealed by
seismology
Earth’s
mantle
structure
beneath an
old ocean
basin:
S-wave
velocity to
depth of
900 km
3. Earth’s internal heat and
temperature
● Heat flow through Earth’s
interior
● conduction (lithosphere)
● convection (mantle and
core)
Topography
of mid-ocean
ridges in the
Atlantic and
Pacific oceans
3. Earth’s internal heat and
temperature
● Temperatures in the Earth
● geothermal gradient
● normally 20 to 30º C / km
● 1300-1400º C at base of
lithosphere
● 3000-6000º C + in core
An estimate
of the geotherm:
temperature
increases with
depth in the
Earth
4. 3-Dimensional structure of the
mantle
● Seismic
tomography
● Earth’s gravity
field
● The geoid
Mantle structure
Mantle structure
Mantle structure
The geoid:
shape of planet Earth
5. Earth’s magnetic field and the
dynamo
● Earth’s dipole field
● complexity of the magnetic
field
● non-dipole field
component
● secular variations in the
field
● magnetic reversals
Change
in the
location
of the
North
magnetic
pole from
1600 to
2000
Earth’s magnetic field and the geodynamo
Earth’s magnetic field and the geodynamo
Earth’s
magnetic
field
and the
geodynamo
Earth’s
magnetic
field
lines
Earth’s
magnetic
field
reversals:
Step 1
Earth’s
magnetic
field
reversals:
Step 2
Earth’s
magnetic
field
reversals:
Step 3
Earth’s
magnetic
field
reversals:
Step 4
5. Earth’s magnetic field and the
dynamo
● Paleomagnetism
● records of magnetization
● thermo-remanent
● depositional remanent
● magnetic stratigraphy
Thermoremanent
Depositional remanent
Depositional remanent
Magnetic stratigraphy
5. Earth’s magnetic field and the
dynamo
●
Magnetic field and the biosphere
● magnetic orientation
● magnetic frame of reference
● field offers protection from
the solar wind